1. Field of the Invention
The invention relates to headers for air-cooled heat exchangers and, more specifically, to a header having a generally square or rectangular unitary body, i.e. a weldless body.
2. Description of the Related Art
Air-cooled heat exchangers are frequently used in industrial applications. A fluid, either a gas or a liquid, is passed through a series of cooling tubes while air is mechanically passed over the exterior of the cooling tubes. The air absorbs heat from the cooling tubes thereby lowering the temperature of the fluid within the tubes. The cooling tubes may include lateral or axial fins to aid in heat transfer.
Heat exchangers typically include two header boxes having the cooling tubes extending therebetween. The header boxes are formed from a hollow body, each of which have a plurality of ports which allow fluid communication with the cooling tubes. One header box is connected to an inlet coupling and, typically, the other header box is connected to an outlet coupling. Within the body, pass plates may be disposed between groups of cooling tubes ports so that, a fluid entering the first header through the inlet conduit must follow a serpentine path, back and forth through the cooling tubes between the headers, to reach the outlet coupling.
Headers have many common cross-sectional shapes, for example, a quadrilateral, that is rectangular or square, round, oval and even obround. There are problems with header boxes of existing art. A quadrilateral header is typically formed by welding flat plates together. Each of the seams between the plates must be welded. These long corner welds result in significant fabrication time and expense. These welds, however, may fail, either in use or in testing prior to use. Additionally, because a quadrilateral header has generally right angle corners at the welds, the header is subject to stress concentrations which are localized along the welds. Thus, because stress concentrations contribute to potential failure of the header, it is preferable to have unwelded or curved surfaces in pressure vessels.
A header having a circular, oval, or obround cross-section does not have a large stress concentrations like a quadrilateral header does. A circular or oval header does, however, have other problems. For example, the cooling tubes are typically parallel to each another. Thus, when drilling cooling tube openings in a circular or oval header, the drill bit must be maintained in single plane, regardless of where on the perimeter the drill is located. Maintaining the alignment of the drill makes drilling difficult at the top and bottom of a circular or oval header. Similarly, it is more difficult to attach cooling tubes to a curved surface than it is to attach the cooling tubes to a flat surface.
Another problem in circular or oval headers is that, where threaded flat head shoulder plugs are used to plug access holes, the flat underside of the plug head does not fully engage the curved surface of the header. Thus, to provide an adequate sealing surface, the header may require spot face machining to provide flat surface for the plug to engage. Machining the header reduces the minimum thickness of the header wall in the area of the plug. Thus, the entire header may have to be manufactured with an additional material thickness to contain a specified pressure.
The invention of the obround header solved some, but not all, of these problems and has its own disadvantages. An obround header has a unitary body with two flat opposing vertical sides which are connected by two curved opposing sides. The openings for the cooling tubes and plugs are located on the two flat sides. Thus, the drilling of the openings for the cooling tubes and the plug is simplified and the cooling tubes and plugs are more easily coupled to the header. Because the header is made from a unitary body, there are no weld seams except at the ends where end plates are attached. The inlet coupling and outlet coupling, however, must still be coupled to one of the curved sides. The coupling must be specially formed to match the curved sides and attaching the coupling to the curved side is difficult. Additionally, the obround shape makes installation of the pass plates more difficult. Also, because the curved sides extend above and below the plane of the cooling tubes, the obround header requires more space than a traditional quadrilateral header.
There is, therefore, a need for a header for a heat exchanger having a unitary body having a quadrilateral cross-sectional shape.
There is a further need for a header for a heat exchanger having one set of opposing, flat sides having openings therethrough which are structured to be coupled to either cooling tubes or plugs, and a second set of opposing, flat sides having openings therethrough that are structured to be coupled to an inlet coupling or an outlet coupling.
These needs, and others, are satisfied by the invention which provides a header box having a unitary body which has a generally hollow, quadrilateral cross-sectional shape. The body has two sets of generally flat, parallel, opposing sides. The openings for the cooling tubes and the plugs are located on one set of opposing sides. An opening for a inlet or outlet coupling is located on one side of the second set of opposing sides. Other openings, e.g., for a temperature probe, may also be located on one of the sides in the second set of opposing sides.